A method is described in German Patent Publication No. 40 35 957, or in the corresponding U.S. Pat. No. 5,201,293, in which a primary-side monitoring of the spark voltage and/or of the spark duration, as a method for detecting ignition misfirings, is so combined with a method for measuring irregular running, as a recognition of combustion misses, that at least one of the two methods will work under every engine operation condition, and that under those engine operation conditions, in which one of the two methods yields inaccurate results, the method yielding inaccurate results is masked out (suppressed), the consequence being that only the other method is performed each time. In those cases, in which both methods are performed, the results of the various methods can be examined in a plausibility check to reduce the risk of faulty monitoring results.
Individual methods for monitoring operations of the internal combustion engine are also described in European Patent Application No. 0 344 349, for example, which shows a primary-side monitoring of the spark duration. A method for detecting irregular operation of the internal combustion engine is described in U.S. Pat. No. 4,691,288.